Write the half equation for the oxygen electrode reaction in a hydrogen fuel cell when the formulae and charges are supplied.

Oxygen half‑reaction mis‑written

Students often write the oxygen electrode half‑reaction as O₂ + 4e⁻ → 2O²⁻ instead of the correct form involving water and protons

The correct oxygen half‑reaction in a hydrogen fuel cell is O₂ + 4H⁺ + 4e⁻ → 2H₂O (or, in alkaline solution, O₂ + 2H₂O + 4e⁻ → 4OH⁻). Ensure the reaction includes the appropriate protons or hydroxide ions and produces water, not oxide ions.